Polymeric and composite parts may be composed of layers of different materials. For some applications, adhesive bonding is sufficient to join the different materials. In other applications, it may be necessary for these dissimilar materials to be chemically bonded together through covalent bonds.
A common combination of dissimilar materials is polyolefins and non-polyolefins. Non-polyolefins may include, for example, thermoplastics, elastomers, thermoplastic elastomers, thermosets, metals, metal oxides, ceramics, alone or in combination. In most cases, it is difficult to covalently bond unmodified polyolefins directly to the non-polyolefins. Therefore, a “tie-layer” is commonly used between the two materials. A tie-layer is often a material that has properties of both the polyolefin and the non-polyolefin. Frequently, the tie-layer has similar melt processing properties as the polyolefin while being chemically reactive toward the non-polyolefin. The chemically reactive properties of the tie-layer may be incorporated during polymerization of the tie-layer, or by secondary reactions on a preformed polymer.
For example, composite tubing may be constructed from layers of dissimilar materials. For some applications, it may be necessary for these dissimilar materials to be chemically bonded together. A common combination of dissimilar materials that may be found in a spoolable tube are polyolefins and non-polyolefins. The non-polyolefinic materials are commonly thermoplastic or thermosetting resins that may be used as a matrix for fibers.
Most commercially available tie-layers for joining polyolefins to non-polyolefins have hydrolytically unstable moieties in the polymer backbone, pendent to the polymer backbone, or created via the reaction of the tie-layer with the non-polyolefin.
Applications for multi-layer or composite parts may require the covalent bonds between the different materials to be stable to water at elevated temperatures. Composite tubing, for example, is frequently used in applications where water or water vapor is present at temperatures greater than 140° F. Under these conditions, the hydrolyzable groups of a tie-layer may be split by the water, thus degrading the polyolefin to non-polyolefin bonding.
Therefore, there is a need for tie-layer materials to join polyolefins to non-polyolefins which do not contain hydrolyzable moieties.